Art collectors love nothing more than being in on the joke. Peter Brant’s striking nude sculpture of his wife Stephanie Seymour, depicted as a ship’s figurehead by artist Maurizio Cattelan, is called Trophy Wife. Steven A. Cohen, Wall Street’s most ruthless profit machine, is the proud possessor of Damien Hirst’s famous 14-foot-long Tiger Shark in a fish tank. And Dakis Joannou has a114-foot-long yachtpainted in a kaleidoscopic pattern of yellow, blue and black byJeff Koons, and christened Guilty.